Polyolefinic compositions

ABSTRACT

A polymer composition comprising (per cent by weight): 
     a) 57%-74%, of a crystalline propylene polymer having an amount of isotactic pentads (mmmm), measured by  13 C-MNR on the fraction insoluble in xylene at 25° C., higher than 97.5 molar % and a polydispersity index ranging from 5 to 10; 
     b) 8 to 15%, of an elastomeric copolymer of ethylene and propylene, the copolymer having an amount of recurring units deriving from ethylene ranging from 30 to 50%, and being partially soluble in xylene at ambient temperature; the polymer fraction soluble in xylene at ambient temperature having an intrinsic viscosity value ranging from 2.5 to 3.5 dl/g; and 
     c) 18-28%, of ethylene homopolymer having an intrinsic viscosity value ranging from 1.5 to 4 dl/g; 
     said composition having a value of melt flow rate ranging from 35 to 60 g/10 min, and the amount of hexane extractables lower than 4.0 wt %.

This application is the U.S. national phase of International ApplicationPCT/EP2010/060461, filed Jul. 20, 2010, claiming priority to EuropeanApplication 09167003.4 filed Jul. 31, 2009 and the benefit under 35U.S.C. 119(e) of U.S. Provisional Application No. 61/274,147, filed Aug.13, 2009; the disclosures of International ApplicationPCT/EP2010/060461, European Application 09167003.4 and U.S. ProvisionalApplication No. 61/274,147, each as filed, are incorporated herein byreference.

The present invention relates to polyolefin compositions having a goodbalance of mechanical properties and a process to prepare saidcompositions. In particular, the compositions exhibits low amount ofhexane extractables so that it is fit for food packaging and the like.

As is known, the isotactic polypropylene, though being endowed with anexceptional combination of excellent properties, is affected by thedrawback of possessing an insufficient impact resistance at relativelylow temperatures.

According to the teaching of the prior art, it is possible to obviatethe said drawback and maintain whitening resistance, without sensiblyaffecting the other polymer properties, by properly adding rubbers andpolyethylene to the polypropylene.

WO 2006/125720 Relates to a Polypropylene Composition Comprising (PerCent by Weight):

a) 65-77%, of a crystalline propylene polymer having an amount ofisotactic pentads (mmmm), measured by ¹³C-MNR on the fraction insolublein xylene at 25° C., higher than 97.5 molar %;

b) 8 to less than 13%, of an elastomeric copolymer of ethylene andpropylene, the copolymer having an amount of recurring units derivingfrom ethylene ranging from 30 to 70%, and being partially soluble inxylene at ambient temperature; the polymer fraction soluble in xylene atambient temperature having an intrinsic viscosity value ranging from 2to 4 dl/g; and

c) 10-23%, of polyethylene having an intrinsic viscosity value rangingfrom 1.5 to 4 dl/g and optionally containing recurring units derivedfrom propylene in amounts lower than 10%.

The composition typically has a value of melt flow rate ranging from0.50 to 10 g/10 min.

WO 2006/067023 Relates to a Polypropylene Composition Comprising (PerCent by Weight):

a) 50-77%, of a crystalline propylene polymer having an amount ofisotactic pentads (mmmm), measured by ¹³CNMR on the fraction insolublein xylene at 25° C., higher than 97.5 molar % and a polydispersity indexranging from 4 to 10;

b) 13-28%, of an elastomeric copolymer of ethylene and propylene, thecopolymer having an amount of recurring units deriving from ethyleneranging from 30 to 70%, being partially soluble in xylene at ambienttemperature, the polymer fraction soluble in xylene at ambienttemperature having an intrinsic viscosity value ranging from 2 to 4dl/g; and

c) 10-22%, preferably 10 to 20%, of polyethylene having an intrinsicviscosity value ranging from 1 to 3 dl/g and optionally containingrecurring units deriving from propylene in amounts up to less than 10%.

The composition typically has a value of melt flow rate ranging from 10to 30 g/10 min.

The applicant found that it is possible to improve the hexaneextractables of similar compositions so that to obtain a material fitfor food applications and at the same time maintaining goodstress-whitening resistance properties by using a polymer compositionhaving certain features.

Thus, an object of the present invention is a polymer compositioncomprising (per cent by weight):

a) 57%-74%, preferably 62% to 71%, of a crystalline propylene polymerhaving an amount of isotactic pentads (mmmm), measured by ¹³C-MNR on thefraction insoluble in xylene at 25° C., higher than 97.5 molar % and apolydispersity index ranging from 5 to 10;

b) 8 to 15%, preferably 9 to 12%, of an elastomeric copolymer ofethylene and propylene, the copolymer having an amount of recurringunits deriving from ethylene ranging from 30 to 50 wt %, preferably 40to 48 wt %, and being partially soluble in xylene at ambienttemperature; the polymer fraction soluble in xylene at ambienttemperature having an intrinsic viscosity value ranging from 2.5 to 3.5dl/g; preferably from 2.5 and 3.0 and

c) 18-28%, preferably 20 to 25%, of ethylene homopolymer having anintrinsic viscosity value ranging from 1.5 to 4 dl/g;

said composition having a value of melt flow rate ranging from 35 to 60g/10 min, preferably 45 to 60 g/10 min, more preferably from 50 to 57g/10 min and the amount of hexane extractables lower than 4.0 wt %,preferably lower than 3.5 wt %.

By ambient temperature and room temperature is meant a temperature of25° C. By elastomeric polymer is meant a polymer having a solubility inxylene at ambient temperature (25° C.) higher than 50 wt %. Bycrystalline propylene polymer is meant a polymer having an amount ofisotactic pentads (mmmm), measured by ¹³C-MNR on the fraction insolublein xylene at 25° C., higher than 97.5 molar %.

Preferably the composition has a content of component (b) plus component(c) in amounts comprised between 25 wt % and 35 wt %.

Typically, the composition of the present invention exhibits a flexuralmodulus value at least 1300 MPa, preferably it is comprised between 1300MPa and 1500 MPa.

Stress-whitening resistance values corresponding to a diameter of thewhitened area of at most 220 mm caused by a ram falling from a 76 cmheight and a diameter of the whitened area of at most 160 mm caused by aram falling from a 20 cm height.

Crystalline propylene polymer (a) is selected from a propylenehomopolymer and a copolymer of propylene containing at most 3 wt % ofethylene or a C₄-C₁₀ α-olefin or combination thereof. Particularlypreferred is the propylene homopolymer.

Typically crystalline propylene polymer (a) shows a molecular weightdistribution, expressed by the ratio between the weight averagemolecular weight and numeric average molecular weight, i.e. M _(w)/ M_(n), measured by GPC, equal to or higher than 7.5, in particular from 8to 20. The melt flow rate of crystalline propylene polymer (a) typicallyranges from 150 to 250 g/10 min, preferably from 180 to 220 g/10 min,more preferably from 190 to 210 g/10 min.

Typically crystalline propylene polymer (a) shows a value of z averagemolecular weight to numeric average molecular weight ratio, i.e. M _(z)/M _(w), measured by GPC, of at least 3.5, preferably 4, more preferably5, for example from 9 to 10.

Elastomeric ethylene-propylene copolymer (b) can optionally comprise adiene. When present, the diene is typically in amounts ranging from 0.5to 10 wt % with respect to the weight of copolymer (b). The diene can beconiugated or not and is selected from butadiene, 1,4-hexadiene,1,5-hexadiene, and ethylidene-norbornene-1, for example.

Elastomeric ethylene-propylene copolymer (b) can optionally comprise adiene. When present, the diene is typically in amounts ranging from 0.5to 10 wt % with respect to the weight of copolymer (b). The diene can beconiugated or not and it is preferably selected from butadiene,1,4-hexadiene, 1,5-hexadiene, and ethylidene-norbornene-1. The intrinsicviscosity of the soluble fraction in xylene at room temperature iscomprised between 1.5 and 4.0 dl/g; preferably between 2.0 and 3.5 dl/g;more preferably between 2.5 and 3.2 dl/g.

Polyethylene (c) is crystalline or semicrystalline and is selected fromethylene homopolymer. The intrinsic viscosity values of copolymer (c)are preferably within the range from 2.0 -3.5 dl/g.

The composition of the present invention is obtained by means of asequential copolymerization process.

Therefore, the present invention is further directed to a process forthe preparation of the polyolefin compositions as reported above, saidprocess comprising at least three sequential polymerization stages witheach subsequent polymerization being conducted in the presence of thepolymeric material formed in the immediately preceding polymerizationreaction, wherein the polymerization stage of propylene to thecrystalline polymer (a) is carried out in at least one stage, than acopolymerization stage of mixtures of ethylene with propylene (andoptionally a diene) to elastomeric polymer (b) and finally apolymerization stage of ethylene to polyethylene (c) are carried out.The polymerisation stages may be carried out in the presence of astereospecific Ziegler-Natta catalyst.

According to a preferred embodiment, all the polymerisation stages arecarried out in the presence of a catalyst comprising a trialkylaluminiumcompound, optionally an electron donor, and a solid catalyst componentcomprising a halide or halogen-alcoholate of Ti and an electron-donorcompound supported on anhydrous magnesium chloride. Catalysts having theabove-mentioned characteristics are well known in the patent literature;particularly advantageous are the catalysts described in U.S. Pat. No.4,399,054 and EP-A-45 977. Other examples can be found in U.S. Pat. No.4,472,524.

Preferably the polymerisation catalyst is a Ziegler-Natta catalystcomprising a solid catalyst component comprising:

a) Mg, Ti and halogen and an electron donor (internal donor),

b) an alkylaluminum compound and, optionally (but preferably),

c) one or more electron-donor compounds (external donor).

The internal donor is preferably selected from the esters of mono ordicarboxylic organic acids such as benzoates, malonates, phthalates andcertain succinates. They are described in U.S. Pat. No. 4,522,930,European patent 45977 and international patent applications WO 00/63261and WO 01/57099, for example. Particularly suited are the phthalic acidesters and succinate acids esters. Alkylphthalates are preferred, suchas diisobutyl, dioctyl and diphenyl phthalate and benzyl-butylphthalate.

Among succinates, they are preferably selected from succinates of theformula (I):

wherein the radicals R₁ and R_(2,) equal to or different from eachother, are a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl,arylalkyl or alkylaryl group, optionally containing heteroatoms; theradicals R₃ to R₆, equal to or different from each other, are hydrogenor a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl,arylalkyl or alkylaryl group, optionally containing heteroatoms, and theradicals R₃ to R₆ which are joined to the same carbon atom can be linkedtogether to form a cycle; with the proviso that when R₃ to R₅ arecontemporaneously hydrogen, R₆ is a radical selected from primarybranched, secondary or tertiary alkyl groups, cycloalkyl, aryl,arylalkyl or alkylaryl groups having from 3 to 20 carbon atoms; or offormula (II):

wherein the radicals R₁ and R₂, equal to or different from each other,are a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl,arylalkyl or alkylaryl group, optionally containing heteroatoms and theradical R₃ is a linear alkyl group having at least four carbon atomsoptionally containing heteroatoms.

The Al-alkyl compounds used as co-catalysts comprise Al-trialkyls, suchas Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclicAl-alkyl compounds containing two or more Al atoms bonded to each otherby way of O or N atoms, or SO₄ or SO₃ groups. The Al-alkyl compound isgenerally used in such a quantity that the Al/Ti ratio be from 1 to1000.

External donor (c) can be of the same type or it can be different fromthe succinates of formula (I) or (II). Suitable external electron-donorcompounds include silicon compounds, ethers, esters such as phthalates,benzoates, succinates also having a different structure from those offormula (I) or (II), amines, heterocyclic compounds and particularly2,2,6,6-tetramethylpiperidine, ketones and the 1,3-diethers of thegeneral formula (III):

wherein R^(I) and R^(II) are the same or different and are C₁-C₁₈ alkyl,C₃-C₁₈ cycloalkyl or C₇-C₁₈ aryl radicals; R^(III) and R^(IV) are thesame or different and are C₁-C₄ alkyl radicals; or the 1,3-diethers inwhich the carbon atom in position 2 belongs to a cyclic or polycyclicstructure made up of 5, 6 or 7 carbon atoms and containing two or threeunsaturations.

Ethers of this type are described in published European patentapplications 361493 and 728769. Preferred electron-donor compounds thatcan be used as external donors include aromatic silicon compoundscontaining at least one Si-OR bond, where R is a hydrocarbon radical. Aparticularly preferred class of external donor compounds is that ofsilicon compounds of formula R_(a) ⁷R_(b) ⁸Si(OR⁹)_(c), where a and bare integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c)is 4; R⁷, R⁸, and R⁹, are C₁-C₁₈ hydrocarbon groups optionallycontaining heteroatoms. Particularly preferred are the silicon compoundsin which a is 1, b is 1, c is 2, at least one of R⁷ and R⁸ is selectedfrom branched alkyl, alkenyl, alkylene, cycloalkyl or aryl groups with3-10 carbon atoms optionally containing heteroatoms and R⁹ is a C₁-C₁₀alkyl group, in particular methyl. Examples of such preferred siliconcompounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane,t-hexyltrimethoxysilane, cyclohexylmethyldimethoxysilane,3,3,3-trifluoropropyl-2-ethylpiperidyl-dimethoxysilane,diphenyldimethoxysilane, methyl-t-butyldimethoxysilane,dicyclopentyldimethoxysilane,2-ethylpiperidinyl-2-t-butyldimethoxysilane,(1,1,1-trifluoro-2-propyl)-methyldimethoxysilane and(1,1,1-trifluoro-2-propyl)-2-ethylpiperidinyldimethoxysilane. Moreover,are also preferred the silicon compounds in which a is 0, c is 3, R⁸ isa branched alkyl or cycloalkyl group, optionally containing heteroatoms,and R⁹ is methyl. Particularly preferred specific examples of siliconcompounds are (tert-butyl)₂Si(OCH₃)₂, (cyclohexyl)(methyl) Si(OCH₃)₂,(phenyl)₂Si(OCH₃)₂ and (cyclopentyl)₂Si(OCH₃)₂.

Preferably electron donor compound (c) is used in such an amount to givea molar ratio between the organoaluminum compound and said electrondonor compound (c) of from 0.1 to 500, more preferably from 1 to 300 andin particular from 3 to 100.

As explained above, the solid catalyst component comprises, in additionto the above electron donors, Ti, Mg and halogen. In particular, thecatalyst component comprises a titanium compound, having at least aTi-halogen bond, and the above mentioned electron donor compoundssupported on a Mg halide. The magnesium halide is preferably MgCl₂ inactive form, which is widely known from the patent literature as asupport for Ziegler-Natta catalysts. Patents U.S. Pat. No. 4,298,718 andU.S. Pat. No. 4,495,338 were the first to describe the use of thesecompounds in Ziegler-Natta catalysis. It is known from these patentsthat the magnesium dihalides in active form used as support orco-support in components of catalysts for the polymerisation of olefinsare characterized by X-ray spectra in which the most intense diffractionline that appears in the spectrum of the non-active halide is diminishedin intensity and is replaced by a halo whose maximum intensity isdisplaced towards lower angles relative to that of the more intenseline.

The preferred titanium compounds are TiCl₄ and TiCl₃; furthermore, alsoTi-haloalcoholates of formula Ti(OR)n−yXy can be used, where n is thevalence of titanium, y is a number between 1 and n, X is halogen and Ris a hydrocarbon radical having from 1 to 10 carbon atoms.

The preparation of the solid catalyst component can be carried outaccording to several methods, well known and described in the art.

According to a preferred method, the solid catalyst component can beprepared by reacting a titanium compound of formula Ti(OR)n−yXy, where nis the valence of titanium and y is a number between 1 and n, preferablyTiCl₄, with a magnesium chloride deriving from an adduct of formulaMgCl₂·pROH, where p is a number between 0.1 and 6, preferably from 2 to3.5, and R is a hydrocarbon radical having 1-18 carbon atoms. The adductcan be suitably prepared in spherical form by mixing alcohol andmagnesium chloride in the presence of an inert hydrocarbon immisciblewith the adduct, operating under stirring conditions at the meltingtemperature of the adduct (100-130° C.). Then, the emulsion is quicklyquenched, thereby causing the solidification of the adduct in form ofspherical particles.

Examples of spherical adducts prepared according to this procedure aredescribed in U.S. Pat. No. 4,399,054 and U.S. Pat. No. 4,469,648. The soobtained adduct can be directly reacted with the Ti compound or it canbe previously subjected to thermally controlled dealcoholation (80-130°C.) so as to obtain an adduct in which the number of moles of alcohol isgenerally lower than 3, preferably between 0.1 and 2.5. The reactionwith the Ti compound can be carried out by suspending the adduct(dealcoholated or as such) in cold TiCl₄ (generally 0° C.); the mixtureis heated up to 80-130° C. and kept at this temperature for 0.5-2 hours.The treatment with TiCl₄ can be carried out one or more times. Theelectron donor compound(s) can be added during the treatment with TiCl₄.

Regardless of the preparation method used, the final amount of theelectron donor compound(s) is preferably such that the molar ratio withrespect to the MgCl₂ is from 0.01 to 1, more preferably from 0.05 to0.5.

The said catalyst components and catalysts are described in WO 00/63261and WO 01/57099.

The catalysts may be precontacted with small quantities of olefin(prepolymerisation), maintaining the catalyst in suspension in ahydrocarbon solvent, and polymerising at temperatures from ambient to60° C., thus producing a quantity of polymer from 0.5 to 3 times theweight of the catalyst. The operation can also take place in liquidmonomer, producing, in this case, a quantity of polymer 1000 times theweight of the catalyst.

By using the above mentioned catalysts, the polyolefin compositions areobtained in spheroidal particle form, the particles having an averagediameter from about 250 to 7,000 microns, a flowability of less than 30seconds and a bulk density (compacted) greater than 0.4 g/ml.

The polymerisation stages may occur in liquid phase, in gas phase orliquid-gas phase. Preferably, the polymerisation of crystalline polymer(a) is carried out in liquid monomer (e.g. using liquid propylene asdiluent), while the copolymerisation stages of elastomeric copolymer (b)and polyethylene (c) are carried out in gas phase. Alternatively, allthe three sequential polymerisation stages can be carried out in gasphase.

The reaction temperature in the polymerisation stage for the preparationof crystalline polymer (a) and in the preparation of elastomericcopolymer (b) and polyethylene (c) be the same or different, and ispreferably from 40 to 100° C.; more preferably, the reaction temperatureranges from 50 to 80° C. in the preparation of polymer (a), and from 70to 100° C. for the preparation of polymer components (b) and (c).

The pressure of the polymerisation stage to prepare polymer (a), ifcarried out in liquid monomer, is the one which competes with the vaporpressure of the liquid propylene at the operating temperature used, andit may be modified by the vapor pressure of the small quantity of inertdiluent used to feed the catalyst mixture, by the overpressure ofoptional monomers and by the hydrogen used as molecular weightregulator.

The polymerisation pressure preferably ranges from 33 to 43 bar, if donein liquid phase, and from 5 to 30 bar if done in gas phase. Theresidence times relative to the two stages depend on the desired ratiobetween polymers (a) and (b) and (c), and can usually range from 15minutes to 8 hours. Conventional molecular weight regulators known inthe art, such as chain transfer agents (e.g. hydrogen or ZnEt₂), may beused.

Conventional additives, fillers and pigments, commonly used in olefinpolymers, may be added, such as nucleating agents, extension oils,mineral fillers, and other organic and inorganic pigments. Inparticular, the addition of inorganic fillers, such as talc, calciumcarbonate and mineral fillers, also brings about an improvement to somemechanical properties, such as flexural modulus and HDT. Talc can alsohave a nucleating effect.

The nucleating agents are added to the compositions of the presentinvention in quantities ranging from 0.05 to 2% by weight, morepreferably from 0.1 to 1% by weight, with respect to the total weight,for example.

The particulars are given in the following examples, which are given toillustrate, without limiting, the present invention.

The following analytical methods have been used to determine theproperties reported in the detailed description and in the examples.

Ethylene: By IR spectroscopy.

Fractions soluble and insoluble in xylene at 25° C.: 2.5 g of polymerare dissolved in 250 mL of xylene at 135° C. under agitation. After 20minutes the solution is allowed to cool to 25° C., still underagitation, and then allowed to settle for 30 minutes. The precipitate isfiltered with filter paper, the solution evaporated in nitrogen flow,and the residue dried under vacuum at 80° C. until constant weight isreached. Thus one calculates the percent by weight of polymer solubleand insoluble at room temperature (25° C.).

Intrinsic Viscosity [η]: Measured in tetrahydronaphthalene at 135° C.

Molecular weight ( M _(n), M _(w), M _(z)): Measured by way of gelpermeation chromatography (GPC) in 1,2,4-trichlorobenzene.

Determination of isotactic pentads content: 50 mg of each xyleneinsoluble fraction were dissolved in 0.5 mL of C₂D₂Cl₄.

The ¹³C NMR spectra were acquired on a Bruker DPX-400 (100.61 Mhz, 90°pulse, 12 s delay between pulses). About 3000 transients were stored foreach spectrum; mmmm pentad peak (21.8 ppm) was used as reference.

The microstructure analysis was carried out as described in literature(Polymer, 1984, 25, 1640, by Inoue Y. et Al. and Polymer, 1994, 35, 339,by Chujo R. et Al.).

Polydispersity index: Determined at a temperature of 200° C. by using aparallel plates rheometer model RMS-800 marketed by RHEOMETRICS (USA),operating at an oscillation frequency which increases from 0.1 rad/secto 100 rad/sec. From the crossover modulus one can derive the P.I. byway of the equation:

P.I.=10⁵/Gc

in which Gc is the crossover modulus which is defined as the value(expressed in Pa) at which G′=G″ wherein G′ is the storage modulus andG″ is the loss modulus.

This method is used for polymers having an MFR value of 20 g/10 min orless.

Polydispersity index: Measurement of molecular weight distribution ofthe polymer. To determine the PI value, the modulus separation at lossmodulus value, e.g. 500 Pa, is determined at a temperature of 200° C. byusing a RMS-800 parallel plates rheometer model marketed by Rheometrics(USA), operating at an oscillation frequency which increases from 0.01rad/second to 100 rad/second. From the modulus separation value, the PIcan be derived using the following equation:

PI=54.6×(modulus separation)^(−1.76)

wherein the modulus separation (MS) is defined as:

MS=(frequency at G′=500 Pa)/(frequency at G″=500 Pa)

wherein G′ is the storage modulus and G″ is the loss modulus.

This method is used for polymers having an MFR value over 20 g/10 min.

Determination of isotactic pentads content: 50 mg of each xyleneinsoluble fraction were dissolved in 0.5 mL of C₂D₂Cl₄.

The ¹³C NMR spectra were acquired on a Bruker DPX-400 (100.61 Mhz, 90°pulse, 12 s delay between pulses). About 3000 transients were stored foreach spectrum; mmmm pentad peak (21.8 ppm) was used as reference.

The microstructure analysis was carried out as described in literature(Polymer, 1984, 25, 1640, by Inoue Y. et Al. and Polymer, 1994, 35, 339,by Chujo R. et Al.).

Melt flow rate: Determined according to ISO method 1133 (230° C. and2.16 kg).

Flexural modulus: Determined according to ISO method 178.

Izod impact resistance: Determined according to ISO method 180/1A.

Stress-whitening resistance: The resistance to whitening is determinedby subjecting to the impact of a ram having a 76 g weight small discs,which have a 4 cm diameter and prepared by injection moulding, preparedfrom the polymer being tested. Both the minimum height (h) up to themaximum height allowed by the apparatus necessary to obtain whitening,and the width (diameter) of the whitened area are recorded.

1640, by Inoue Y. et Al. and Polymer, 1994,35,339, by Chujo R. et Al.).

Polydispersity index: Measurement of molecular weight distribution ofthe polymer. To determine the PI value, the modulus separation at lossmodulus value, e.g. 500 Pa, is determined at a temperature of 200° C. byusing a RMS-800 parallel plates rheometer model marketed by Rheometrics(USA), operating at an oscillation frequency which increases from 0.01rad/second to 100 rad/second. From the modulus separation value, the PIcan be derived using the following equation:

PI=54.6×(modulus separation)^(−1.76)

wherein the modulus separation (MS) is defined as:

MS=(frequency at G′=500 Pa)/(frequency at G″=500 Pa)

wherein G′ is the storage modulus and G″ is the loss modulus.

This method is used for polymers having an MFR value over 20 g/10 min.

TREF Method for the Separation of Polyethylene

The column used was a stainless steel fractionating column filled withpennax glass beads with 1-1.2 mm diameter.

About 1.5 g of the purified sample was dissolved in hot o-xylene. Thesolution was loaded in the TREF column and then a slow cooling programwas applied. Every elution step was performed at a constant temperatureand flow rate (10 ml/min). The flow was interrupted to allow thermalequilibrium to be reached. Five fraction are collected at differenttemperatures by using o-xylene(fraction 1, 3-5) and butoxyethanol(fraction 2). The fractionation temperatures were respectively 25° C.,138° C., 90° C., 100° C. and 125° C. Fraction 4 eluted at 100° C. wastaken as the polyethylene fraction.

EXAMPLE 1

In a plant operating continuously according to the mixed liquid-gaspolymerization technique, runs were carried out under the conditionsspecified in Table 1.

The polymerization was carried out in the presence of a catalyst systemin a series of three reactors equipped with devices to transfer theproduct from one reactor to the one immediately next to it.

Preparation of the Solid Catalyst Component

Into a 500 ml four-necked round flask, purged with nitrogen, 250 ml ofTiCl₄ are introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂·1.9C₂H₅OH (prepared according to the method described in ex.2 ofU.S. Pat. No. 4,399,054 but operating at 3000 rpm instead of 10000 rpm)and 9.1 mmol of diethyl 2,3-(diisopropyl)succinate are added. Thetemperature is raised to 100° C. and maintained for 120 min. Then, thestirring is discontinued, the solid product was allowed to settle andthe supernatant liquid is siphoned off. Then 250 ml of fresh TiCl₄ areadded. The mixture is reacted at 120° C. for 60 min and, then, thesupernatant liquid is siphoned off. The solid is washed six times withanhydrous hexane (6×100 ml) at 60° C.

Catalyst System and Prepolymerization Treatment

The solid catalyst component described above was contacted at 12° C. for24 minutes with aluminium triethyl (TEAL) anddicyclopentyldimethoxysilane (DCPMS) as outside-electron-donorcomponent. The weight ratio between TEAL and the solid catalystcomponent and the weight ratio between TEAL and DCPMS are specified inTable 1.

The catalyst system is then subjected to prepolymerization bymaintaining it in suspension in liquid propylene at 20° C. for about 5minutes before introducing it into the first polymerization reactor.

Polymerization

The polymerisation run is conducted in continuous in a series of threereactors equipped with devices to transfer the product from one reactorto the one immediately next to it. The first reactor is a liquid phasereactor, and the second and third reactors are fluid bed gas phasereactors. Polymer (a) is prepared in the first reactor, while polymers(b) and (c) are prepared in the second and third reactor, respectively.

Temperature and pressure are maintained constant throughout the courseof the reaction. Hydrogen is used as molecular weight regulator.

The gas phase (propylene, ethylene and hydrogen) is continuouslyanalysed via gas-chromatography.

At the end of the run the powder is discharged and dried under anitrogen flow. The polymerization conditions are reported in table 1.

The propylene compositions were added with the following additivesIrgafos 168, 800 ppm Atmer 163, 10000 ppm GMS 90, 900 ppm Na Benzoate.The previously said Irganox 1010 is pentaerytrityl tetrakis3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate, while Irgafos 168 istris (2,4-di-tert-butylphenyl) phosphite, both marketed by Ciba-Geigy.

Then the polymer particles are introduced in a twin screw extruderBerstorff (L/D=33).

Temperature of the feeding section: 190-210° C.

Melt temperature: 240° C.

Temperature of the die section: 230° C.

Flow rate: 16 Kg/h

Totational speed: 250 rpm

The polymer features are reported in table 2

TABLE 1 Polymerization Process Example 1 TEAL/solid catalyst component 8weight ratio TEAL/DCPMS weight ratio 5 Liquid phase reactorPolymerisation temperature ° C. 70 Pressure Barg 39.6 Residence timeminutes 73 H2 bulk molppl 8300 1st gas phase reactor Polymerisationtemperature ° C. 80 Pressure Barg 14 Residence time min 10 C2-/(C2- +C3-) Mol ratio 0.28 H2/C2 Mol ratio 0.058 2nd gas phase reactorPolymerisation temperature ° C. 100 Pressure Barg 13 Residence time Min18 C2-/(C2- + C3-) Mol ratio 0.97 H2/C2 Mol ratio 0.15 H2 bulk =hydrogen concentration in the liquid monomer; C2- = ethylene; C3- =Propylene

TABLE 2 Example 1 Component a) Homopolymer content % 69 MFR “L” g/10′200 Xylene soluble fraction % 3.0 Pentad content of the xylene molar% >97.5 insoluble fraction Component b) Copolymer content % 10 Ethylenecontent in % 44 component b) Intrinsic viscosity Xylene dl/g 2.6 solublefraction* Component c) Polyethylene content % 21 Intrinsic viscosity ofdl/g 2.0-3.5 polyethylene** Properties of the composition Ethylenecontent % 25 Xylene -soluble fraction % 13 MFR g/10' 54 Flexural ModulusMPa 1425 Izod at 23° C. kJ/m² 4.5 Izod at 0° C. kJ/m² 3.7 Izod at −20°C. kJ/m² 4.3 D/B TT ° C. −45 Tens. Str. @ yield MPa 24.3 Elong. @ yield% 3.1 Tens. Str. @ break MPa 23.9 Elong. @ break % 6.0 Hexane - extr.(on Film) powder % 3.3 Whitening resistance:  5 cm height mm 80 diameter(mm*10) of 10 cm height mm 110 the whitening area 20 cm height mm 150due to a ram falling 30 cm height mm 170 from a 76 cm height mm 200*calculated taking into account the intrinsic viscosity and the amountof the xylene soluble fraction of component a) **measured on fraction 4after TREF fractionation of the composition

COMPARATIVE EXAMPLE 1

Example 3 of wo2006/067023 was repeated and the hexane solubles has beenmeasured they resulted to be 6.2 wt %

1. A polymer composition comprising (per cent by weight): a) 57%-74%, ofa crystalline propylene polymer having an amount of isotactic pentads(mmmm), measured by ¹³C-MNR on the fraction insoluble in xylene at 25°C., higher than 97.5 molar %; b) 8 to 15%, of an elastomeric copolymerof ethylene and propylene, the copolymer having an amount of recurringunits deriving from ethylene ranging from 30% to 50%, and beingpartially soluble in xylene at ambient temperature; the polymer fractionsoluble in xylene at ambient temperature having an intrinsic viscosityvalue ranging from 2.5 to 3.5 dl/g; and c) 18-28%, of ethylenehomopolymer having an intrinsic viscosity value ranging from 1.5 to 4dl/g; said composition having a value of melt flow rate ranging from 35to 60 g/10 min, and the amount of hexane extractables lower than 4.0 wt%.
 2. The polymer composition according to claim 1 wherein crystallinepropylene (a) is from 62 to 71 wt %, elastomeric copolymer (b) is from 9to 12 wt % and polyethylene (c) is from 20 to 25 wt % with respect tothe whole polymer composition.
 3. The polymer composition according toclaim 1 wherein the composition has a content of component (b) pluscomponent (c) in amounts of between 25 wt % and 35 wt %,
 4. Apolymerization process for the preparation of the polymer compositionsof claim 1, comprising polymerizing in at least three sequentialpolymerisation stages wherein crystalline polymer (a), elastomericpolymer (b) and polyethylene (c) are prepared in separate subsequentstages, operating in each stage, except the first step, in the presenceof the polymeric material formed and the catalyst used in theimmediately preceding polymerisation stage.